XInput 2 Multi-touch maxing out at 32 touch-points

Peter Hutterer peter.hutterer at
Thu May 14 06:59:30 UTC 2020

On Tue, May 12, 2020 at 04:06:17PM -0600, Alex Averill wrote:
> Hello,
> I am currently working on building an application using XInput 2 and
> RawTouch events to capture touch positions and pass them to another
> application. I am using a 3M Touchscreen that is reporting through X11 that
> it supports 80 points, however I am only ever able to capture at most 32
> touchpoints.

32 sounds suspiciously like a mask somewhere but I couldn't find
anything skimming over the relevant bits.. Are you getting 32 slots from
the device though? libinput record will tell you, look at the
ABS_MT_SLOT value and inside that the ABS_MT_TRACKING_ID. Any slot with
a tracking ID != -1 has a current touch, check how many you can produce.
libinput record output is YAML and easy enough to parse.


> Is there an inherent limit to the total number of
> touchpoints/RawTouchEvents supported by XInput 2?
> Thanks,
> Alex Averill

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